Sid Davidoff, a lawyer who joined John V. Lindsay’s youth-driven campaign for mayor of New York in 1965 and, after victory in the election, became one of Lindsay’s chief lieutenants in City Hall, died on Nov. 16 in the Dominican Republic. He was 86.

Mr. Davidoff’s knowledge of the city’s streets — gleaned, in part, from driving a truck to sell the insecticide DDT to tenement dwellers, waiting tables, and booking rock ‘n’ roll bands — paid off when he shepherded Mr. Lindsay around during the 1965 campaign.

Mr. Davidoff met Mr. Lindsay when, as a young congressman, Mr. Lindsay spoke at NYU. “I knew he was going somewhere,” Mr. Davidoff told The New York Times in an interview in 1967.

After Mr. Lindsay was elected, Mr. Davidoff’s first job with the city was as an assistant buildings commissioner. “I came into my office,” he recalled, “and a civil servant said, ‘Can I help you, sonny?’ “yes,” I said, ‘you’re sitting at my desk.’”

When reporters questioned his credentials for the job, Mr. Davidoff was unfazed. “I’ve lived in buildings all my life,” he said.